Central buffer couplings have been used in series ET 420 urban railway multiple units in which an approximately semicircular channel, in which the electric heater is installed, is made in the buffer surface of the coupling head in the area of the centering ball and the inlet funnel. The heating element is intended to keep the face surface and coupling mechanism free of ice and snow in the winter and ensure the coupling function. The channel is sealed toward the outside by a hard solder, which forms a part of the buffer surface. Only low-melting-point hard solders, such as expensive silver solders, can be used as hard solders, because there is a risk of damaging the heating element at high processing temperatures. The use of soft solders with low melting points proved to be unsuitable because the melting temperature of the soft solder could be reached at the necessary heat output. When soldering in the heating element, there is always the risk of local overheating and resulting destruction of the heating element before placement into service. In addition, soldering in the heater without cavities in the filling material can be ensured only with considerable cost. In the cavities to be avoided, there may be local overheating of the heater on the one hand, or moisture can penetrate during operation, which leads to corrosion.
Further, it is prior art to cover the channel in the faceplate, in which the heating element is placed, toward the outside by welded-in or soldered-in cover sheets. As a result of the increased addition of heat during welding or soldering, a possible distortion or change in the material characteristics of both the cover sheet and the faceplate must be paid attention to and taken into consideration. Because the channel is made much wider than the diameter of the heating element for assembly reasons, there are undefined positionings of the heating element on the inside of the channel, which can lead to heat accumulation and overheating and consequently to destruction of the heating element. In addition to potential damage of the installed heating element by the welding/soldering process itself, in the cavity for the heating element there is always the risk of the penetration of moisture and the resulting destruction of the heater.
An electric heater for central buffer couplings, whose heating element in the channel is filled with a silicon material that forms the outside covering and that is a free-flowing single-component material during filling which cross-links and hardens under the influence of humidity in the air at room temperature, is known from DE 296 11 148 U. Due to the relatively poor heat conduction λ=0.21 W/(m×K) and the poor temperature resistance of the elastic casting compounds that were previously available and used, overheating of the heating element can occur which leads to destruction of the casting compound and consequently to destruction of the heating element. In addition, with the low surface strength of such casting compounds, there is the risk of penetration of foreign bodies and therefore of mechanical damage to the heating element.
Another disadvantage of the aforementioned designs is that replacing defective heating elements, since coiled tubing heating elements are generally used, is possible only by costly separation of the soldering seams or casting compound in the manufacturing plant or at a workshop. After replacing defective heating elements, the systems that are used must again undergo costly manufacturing by further soldering/welding or casting.
Therefore, the aim of the invention is to construct an electric heater for the coupling head of a central coupling buffer in such a way that the transfer of heat from the heating element into the coupling head is improved and the expense of assembly and disassembly of the heating element is reduced.